An electrophotographic apparatus

Abstract: An electrophotographic apparatus, wherein a photoconductor drum (14) with a magnet (15) fixed therein formed with an electrostatic latent image is brought into contact with a magnetic developer (20) in a developer reservoir (19) to have the photoconductor drum (14) surface attached with the developer (20) by magnetic force and further passed a removing roller (21) having an AC voltage (23) applied thereto with resultant development of images because toner remains at image areas only, and which has a structure comprising two magnetic poles (15,22) inside either the photoconductor drum (14) or the removing roller (21), or a means for increasing friction force of the surface either of the photoconductor drum (14) or the removing roller (21).

Description: The present invention relates to an electrophtographic apparatus which can be used in printers, facsimile equipment or the like. A two-component development method using a developer formed of toner and carrier has so far been widely used in electrophotography, but in recent years development of a mono-component development method has been in progress in order to make image forming units smaller and less costly. Fig. 28 shows the electrophotographic apparatus which uses such a mono-component development method and was disclosed by the inventors of the present invention in the Japanese Laid-Open Patent H 6-43759. In Fig. 28, item 1 is an electrostatic latent image holding member of an organic photoconductor drum which has phthalocyanine dispersed in a binder resin of polyester group. Item 2 is a magnet with the axis thereof fixed coaxially with the organic Photoconductor drum 1. Item 3 is a corona charger for charging the organic photoconductor drum 1. Item 4 is a grid electrode for controlling charge potential of the organic Photoconductor drum 1. Item 5 is signal light. Item 6 is a developer reservoir. Item 7 is a magnetic one-component toner serving as developer. Item 8 is a damper for making smooth the flow of the toner 7 inside the developer reservoir 6, and also preventing the toner 7 from being packed due to its own weight and filling between the organic photoconductor drum 1 and a removing roller 9. The magnet 2 forms a magnetic pole in an area of  = 10° opposite to the developer reservoir 6. Item 9 is a removing roller made of aluminum and having a magnet 10 therein. Item 11 is an AC high voltage power source for applying a voltage to the removing roller 9. Item 12 is a scraper made of polyester film for scraping toner from the removing roller 9. Item 13 is a transfer corona charger for transferring toner images formed on the organic photoconductor drum 1 to paper. An explanation will be made hereunder on how said electrophotographic apparatus operates with the help of Fig. 28. The organic photoconductor drum 1 is charged to -500 V by means of the corona charger 3 and the grid electrode 4. An electrostatic latent image is formed by irradiating laser light 5 on the organic photoconductor drum 1. The toner 7 is deposited on the surface of the organic photoconductor drum 1 by magnetic force in the developer reservoir 6. Next, the organic photoconductor drum 1 is caused to pass the front of the removing roller 9. At this time, an AC voltage of 750 0-p (1 kHz in frequency) with a DC voltage of -350 V superimposed thereon is applied to the removing roller 9 from the AC high voltage power source 11. Then, the toner 7 is removed from the organic photoconductor drum 1 to the removing roller 9, and toner images with a positive-negative picture reversal are left only on the image areas of the organic photoconductor drum 1. The toner 7 deposited on the removing roller 9 which is rotating in the arrow direction is scraped off by the scraper 12, and returned to the developer reservoir 6 for use in the image forming steps to follow. The toner images thus formed on the organic photoconductor drum 1 are transfered to paper (not shown in Fig. 28) by the transfer charger 13, and then thermally fixed by means of fixing equipment (not shown in Fig. 28). However, when printing is performed by said electrophotographic apparatus, the image density of solid image is low under a high temperature and high humidity environment (33°C, 85 % RH, for example), and background development is found to increase gradually on the printed images. An electrophotographic apparatus having the features of the preamble of claim 1 is known from EP-A-0 509 441. The object of the present invention is to provide an electrophotographic apparatus for reproducing prints with high image density and excellent image quality not showing any non-uniformity in image density and any background development, either. This object is achieved with an electrographic apparatus having the features of claim 1. In the electrophotographic apparatus according to the invention the developer, e.g. the toner, attached on the electrostatic latent image holding member is transported in abundance to the image development areas where the electrostatic latent image holding member and the removing roller are situated opposite to each other, resulting in an improvement in low image density caused by insufficient supply of toner and in an achievement in gaining a high resolution picture of excellent quality in a stable manner even under the conditions of high temperature and high humidity, and further in an achievement in realizing a picture of excellent quality even when operated under a high speed Processing condition. Furthermore, the toner collected on the removing roller is quickly removed from the image developing areas with resultant prevention of background developing caused by insufficient removing of the toner, consequently contributing to gaining a high resolution picture of excellent quality in a stabilized manner even under the conditions of high temperature and high humidity, and further realizing a picture of excellent quality even when operated under a high speed processing condition. Preferred embodiments form the subject matter of the appended subclaims. Thus, it has become possible to realize an electrophotographic apparatus wherein the quantity of the toner to be deposited on the electrostatic latent image holding member is sufficiently secured with a resultant contribution to gaining a high resolution picture of excellent quality in a stabilized manner even under the conditions of high temperature and high humidity, and further realizing a picture of excellent quality even when operated under a high speed processing condition. Fig. 1 is a schematic illustration to show the structure of a first exemplary embodiment of an electrophotographic apparatus. Fig. 2 is an enlarged view of the vicinity of the developing areas shown in Fig. 1 for explaining effects of the present invention. Fig. 3 is a chart of the magnetic flux density distribution observed in the vertical direction on the surface of the electrostatic latent image holding members of a first, fifth, and sixth exemplary embodiment respectively. Fig. 4 is a schematic illustration for explaining the arrangement of the magnetic poles formed by magnets as described in a first exemplary embodiment. Fig. 5 shows waveforms of the AC voltage as used in a first, second, third, fourth, fifth, sixth, seventh, eighth, and ninth exemplary embodiment respectively. Fig. 6 is a schematic illustration to show the structure of a second exemplary embodiment of an electrophotographic apparatus. Fig. 7 is a chart of the magnetic flux density distribution observed in the vertical direction on the surface of the electrostatic latent image holding member of a second, and seventh exemplary embodiment respectively. Fig. 8 is a schematic illustration for explaining the arrangement of the magnetic poles formed by magnets as described in a second exemplary embodiment. Fig. 9 is a schematic illustration to show the structure of a third exemplary embodiment of an electrophotographic apparatus. Fig. 10 is an enlarged view of the vicinity of the developing areas shown in Fig. 9 for explaining effects of the present invention. Fig. 11 is a chart of the magnetic flux density distribution observed in the vertical direction on the surface of the removing rollers of a third, fifth, and seventh exemplary embodiment respectively. Fig. 12 is a schematic illustration for explaining the arrangement of the magnetic poles formed by magnets as described in a third exemplary embodiment. Fig. 13 is a schematic illustration to show the structure of a fourth exemplary embodiment of an electrophotographic apparatus. Fig. 14 is a chart of the magnetic flux density distribution observed in the vertical direction on the surface of the removing rollers of a fourth, and sixth exemplary embodiment, respectively. Fig. 15 is a schematic illustration for explaining the arrangement of the magnetic poles formed by magnets as described in a fourth exemplary embodiment. Fig. 16 is a schematic illustration to show the structure of a fifth exemplary embodiment of an electrophotographic apparatus, this embodiment being in accordance with the present invention. Fig. 17 is a schematic illustration for explaining the arrangement of the magnetic poles formed by magnets as described in the fifth exemplary embodiment. Fig. 18 is a schematic illustration to show the structure of a sixth exemplary embodiment of an electrophotographic apparatus, this embodiment being in accordance with the present invention. Fig. 19 is a schematic illustration for explaining the arrangement of the magnetic poles formed by magnets as described in the sixth exemplary embodiment. Fig. 20 is a schematic illustration to show the structure of a seventh exemplary embodiment of an electrophotographic apparatus, this embodiment being in accordance with the present invention. Fig. 21 is a schematic illustration for explaining the arrangement of the magnetic poles formed by magnets as described in the seventh exemplary embodiment. Fig. 22 is a schematic illustration to show the structure of an eighth exemplary embodiment of an electrophotographic apparatus. Fig. 23 is a schematic illustration to show the structure of a ninth exemplary embodiment of an electrophotographic apparatus. Fig. 24 is an enlarged cross-sectional view of the surface of the removing roller as described in the ninth exemplary embodiment. Fig. 25 is a schematic illustration to show the structure of a tenth exemplary embodiment of an electrophotographic apparatus. Fig. 26 is a schematic illustration to show the structure of an eleventh exemplary embodiment of an electrophotographic apparatus. Fig. 27 is a schematic illustration to show the structure of a twelfth exemplary embodiment of an electrophotographic apparatus, this embodiment being in accordance with the present invention. Fig. 28 is a schematic illustration to show the structure of a prior art electrophotographic apparatus. A detailed description will be given to the present invention hereunder with the help of examples. In this specification, if a direction of rotation of the first member is specified to be opposite to a direction of rotation of a second member, it is to be understood in that the two members have the same sense of rotation, such that the surface portions of the two members coming closest to each other move in opposite directions, for example, as shown in Figures 1, 2, 6, 9, 10, 13, 16, 18, 20, 22, 23, and 25 to 27. A detailed description will be given to the present invention hereunder with the help of examples. Example 1 An electrophotographic apparatus will be explained as a first exemplary embodiment with the help of Fig. 1 to Fig. 5. Fig. 1 is a schematic illustration to show the structure of Example 1. In Fig. 1, item 14 is a cylindrical electrostatic latent image holding member (30 mm in diameter), which has its surface disposed with an organic Photoconductor Prepared by dispersing phthalocyanine in a binder resin of polyester group, and rotates at a peripheral speed of 30 mm/s. Item 15 is a magnet which is fixed coaxially with said electrostatic latent image holding member 14 formed of non-rotary two poles, and serving as a magnetic field generating means. There are no particular restrictions imposed on the magnet 15, and a permanent magnet or an electromagnet can be used. Item 16 is a corona charger for charging negatively the electrostatic latent image holding member 14. Item 17 is a grid electrode for controlling the charge potential of the electrostatic latent image holding member 14. Item 18 is signal light for forming electrostatic latent images. Item 19 is a developer reservoir. Item 20 is a developer, e.g. a magnetic mono-component negatively chargeable toner with an average particle diameter of 12 µm. Item 21 is a cylindrical removing roller (16 mm in diameter) made of aluminum, and serving as an electrode, which is installed at a specified distance apart from the electrostatic latent image holding member 14 and rotates at a peripheral speed of 30 mm/s in the direction opposite to the rotation of the electrostatic latent image holding member 14. Item 22 is a non-rotary magnet fixed coaxially with the removing roller 21, serving as a magnetic field generating means. There are no specific restrictions imposed on the magnet 22, and a permanent magnet or an electromagnet can be used. Item 23 is an AC high voltage power source for applying a voltage to the removing roller 21. Item 24 is a scraper made of polyester film for scraping off the toner attached on the removing roller 21. Item 25 is a transfer corona charger for transferring the images, which are formed on the electrostatic latent image holding member by deposition of toner, onto paper. Item 26 is a cleaner for removing the toner that remained on the electrostatic latent image holding member 14 after transferring the images. Fig. 3 shows a chart of magnetic flux density distribution observed in the vertical direction on the surface of the electrostatic latent image holding member 14 in the vicinity of the magnet 15. The peak values of the magnetic flux density measure -700 Gs (S-pole), and 500 Gs (N-pole), respectively. The peak value of magnetic flux density of the magnet 22 measures 600 Gs (N-pole) at the surface of the removing roller 21. Fig. 4 shows the positional relation between the magnets 15 and 22 both installed inside the electrostatic latent image holding member 14 and the removing roller 21, respectively. The angle  1 that the south pole of the magnet 15 installed inside the electrostatic latent image holding member 14 makes from the point where the surface of the electrostatic latent image holding member 14 comes closest to that of the removing roller 21 was set to  1 = 40° in the direction opposite to the rotation of the electrostatic latent image holding member 14, while the angle  2 of the north pole being set to  2 = 10°. The angle  3 that the magnet 22 installed inside the removing roller 21 makes from the point where the surface of the removing roller 21 comes closest to that of the electrostatic latent image holding member 14 was set to  3 = -15° in the direction opposite to the rotation of the removing roller 21. The range of said angle  1 is desirable to be 15° <  1 < 50° and the range of 20° <  1 < 45°, in particular, is the most suitable range. The range of  2 is desirable to be 0° <  2 < 30° and the range of 5° <  2 < 20°, in particular, is the most suitable range. The range of  3 is desirable to be -30° <  3 < 10° and the range of -20° <  3 < 0°, in particular, is the most suitable range. The composition of the developer used in present example, e.g. the one component magnetic toner, was 70 % wt. of polyester resin, 25 % wt. of ferrite, 3 % wt. of carbon black, and 2 % wt. of oxycarboxylic acid metal complex with 0.4 % wt. of colloidal silica added further. How the electrophotographic apparatus thus structured operates will be explained hereunder with the help of Fig. 1. The electrostatic latent image holding member 14 was charged to - 500 V by means of the corona charger 16 and the grid electrode 17. (The applied voltage was - 4 kV and the grid electrode voltage was - 500 V.) Then, an electrostatic latent image was formed by irradiation of the laser signal light 18 on said electrostatic latent image holding member 14. At this time, the exposure potential (V r ) of the electrostatic latent image holding member 14 was - 100 V. Next, the one-component magnetic toner was attached on the surface of said electrostatic latent image holding member 14 in the developer reservoir 19 by the magnetic force of the magnet 15. At this time, the toner was charged to about -3 µC/g. The toner attached on the electrostatic latent image holding member 14 was then formed into a brush-like shape along the magnetic force which was produced by the magnet 15 and disposed in the peripheral direction of the electrostatic latent image holding member 14. The said toner attached in the brush-like shape was transported by the frictional force caused by rotation of the electrostatic latent image holding member 14. Thus, the magnetic toner which was aligned along the magnetic force lines produced by magnetic field looks like a brush, and is referred to as a magnetic brush. The electrostatic latent image holding member 14 attached with a toner layer passed the front of the removing roller 21, the surface of which was located at a distance of 300 µm from that of the electrostatic latent image holding member 14. An AC voltage (1 kHz in frequency) of 750 V 0-p superimposed with a DC voltage of - 300 V having a waveform as shown in Fig. 5 was applied to the removing roller 21 from the high voltage power source 23. While the toner layer on the electrostatic latent image holding member 14 was traveling by passing between the electrostatic latent image holding member 14 and the removing roller 21, the toner attached on the non-image areas of the electrostatic latent image holding member 14 was gradually removed to the side of the removing roller 21. There remained only at the image areas of the electrostatic latent image holding member 14 the toner images with a positive-negative picture reversal. The toner attached on the removing roller 21 was formed into a brush-like shape along the magnetic force which was produced by the magnet 22 and disposed in the peripheral direction of the removing roller. The toner attached on the removing roller 21 was transported by the rotation made in the direction indicated by an arrow in Fig. 1, scraped off by the scraper 24, and returned into the developer reservoir 19. It was observed at the upper area of the S-pole on the surface of the electrostatic latent image holding member 14 that the toner was in a fierce turbulence. The toner images thus formed on the electrostatic latent image holding member 14 were transferred on paper (not shown in Fig.1) by means of the transfer corona charger 25. Then, after thermal fixing by means of fixing equipment (not shown in Fig. 1), printed images were obtained. On the other hand, the toner left on the electrostatic latent image holding member 14 after transferring was transported by the rotation of the electrostatic latent image holding member 14, and collected by the cleaner 26. As a result, sharp images of high image density without showing any non-uniformity of density were obtained. Accordingly, this particular exemplary embodiment features a structure comprising a fixed and non-rotary magnet, e.g. a magnetic field generating means, which is installed inside a rotary electrostatic latent image holding member, and produces two magnetic poles having polarity opposite to each other on the surface of the electrostatic latent image holding member in the vicinity of the developing areas where the electrostatic latent image holding member comes closest to the removing roller. How the electrophotographic apparatus of the present example operates and the effects thereof will be explained in a greater detail with the help of Fig. 2. Fig. 2 is an enlarged view to show schematically the vicinity of the developing areas of the electrophotographic apparatus as illustrated in Fig. 1. As shown in Fig. 2, the toner is aligned in a brush-like shape along the magnetic force lines generated by the magnet 15 in the peripheral direction of the electrostatic latent image holding member 14 to form a magnetic brush 20a. Therefore, because the transporting force of the toner 20 exerted by the electrostatic latent image holding member 14 does not work on the individual particles of the toner, which are forming the first layer of the toner and are in direct contact with the surface of the electrostatic latent image holding member, but works on the entire magnetic brush which is a collection of the toner particles put together by magnetic force, the transporting force to carry the toner will be remarkably intensified. Besides, the unevenness in transporting force due to the non-uniformity in frictional force among the individual toner particles will be rectified. As a result, the toner furnished to the electrostatic latent image holding member 14 is supplied to the developing areas in abundance and in a stabilized manner, and excellent picture quality showing a high image density and not having any non-uniformity of density. Example 2 Now, a second exemplary embodiment for an electrophotographic apparatus will be explained with the help of Fig. 6, Fig. 7, and Fig. 8. The present example is a modification of the previous exemplary embodiment, e.g. Example 1, and the structure thereof is illustrated in Fig. 6. The structure shown in Fig. 6 differs from that of Fig. 1 in the magnetic field generating means. More specifically, the magnet 15 installed inside the electrostatic latent image holding member has one magnetic pole, and a magnetic plate 27 has been added, instead, to the magnet 15 at the side opposite to the direction of rotation thereof. As the magnetic plate 27 is used such a substance readily magnetized by an external magnetic field as iron or the like. The other parts of Fig. 6 are the same as those in Fig. 1. Therefore, the same explanation as was made on the symbols used in Fig. 1 applies to those of Fig. 6. Fig. 7 shows a chart of the magnetic flux density distribution of the magnet 15 and the magnetic plate 27 observed in the vertical direction on the surface of the electrostatic latent image holding member 14. The peak values of the magnetic flux density measure -300 Gs (magnetic plate), and 500 Gs (N-pole), respectively. The magnetic plate 27 is magnetized by the magnet 15, and a magnetic pole opposite to the one formed on the surface of the magnet 25 is produced on the surface of the magnet 27. Fig. 8 shows the arrangement of the magnet 15 and the magnetic plate 27 both installed inside the electrostatic latent image holding member 14, and the magnet 22 inside the removing roller 21. The angle  1 that the magnetic 15 installed inside the electrostatic latent image holding member 14 makes from the point where the surface of the electrostatic latent image holding member 14 comes closest to that of the removing roller 21 was set to  1 = 40° in the direction opposite to the rotation of the electrostatic latent image holding member 14, while the angle  2 of the north pole of the magnet 15 inside the electrostatic latent image holding member 14 being set to  2 = 10°. The angle  3 that the north pole of the magnet 22 installed inside the removing roller 21 makes from the point where the surface of the removing roller 21 comes closest to that of the electrostatic latent image holding member 14 was set to  3 = -15° in the direction opposite to the rotation of the removing roller 21. The range of said angle  1 is desirable to be 15° <  1 < 50° and the range of 20° <  1 < 45°, in particular, is the most suitable range. The range of  2 is desirable to be 0° <  2 < 30° and the range of 5° <  2 < 20°, in particular, is the most suitable range. The range of  3 is desirable to be - 30° <  3 < 10° and the range of - 20° <  3 < 0°, in particular, is the most suitable range. How the electrophotographic apparatus thus structured operates will be explained hereunder with the help of Fig. 6. The electrostatic latent image holding member 14 was charged to - 500 V by means of the corona charger 16 and the grid electrode 17. (The applied voltage was - 4 kV and the grid electrode voltage was - 500 V.) Then, an electrostatic latent image was formed by irradiation of the laser signal light 18 on said electrostatic latent image holding member 14. At this time, the exposure potential (V r ) of the electrostatic latent image holding member 14 was - 100 V. Next, the mono-component magnetic toner was attached on the surface of said electrostatic latent image holding member 14 in the developer reservoir 19 by the magnetic force of both the magnet 15 and the magnetic plate 27. The toner attached on the electrostatic latent image holding member 14 was then formed into a brush-like shape along the magnetic force which was produced by both the magnet 15 and the magnetic plate 27, and disposed in the peripheral direction of the electrostatic latent image holding member 14. The said toner attached in the brush-like shape was transported by the frictional force caused by rotation of the electrostatic latent image holding member 14. The electrostatic latent image holding member 14 with the toner layer attached passed the front of the removing roller 21, the surface of which was located at a distance of 300 µm from that of the electrostatic latent image holding member 14. An AC voltage (1 kHz in frequency) of 750 V 0-p superimposed with a DC voltage of - 300 V having a waveform as shown in Fig. 5 was applied to the removing roller 21 from the high voltage power source 23. While the toner layer on the electrostatic latent image holding member 14 was traveling by passing between the electrostatic latent image holding member 14 and the removing roller 21, the toner attached on the non-image areas of the electrostatic latent image holding member 14 was gradually removed to the side of the removing roller 21. There remained only at the image areas of the electrostatic latent image holding member 14 the toner images with a positive-negative picture reversal. The toner attached on the removing roller 21 was formed into a brush-like shape along the magnetic force which was produced by the magnet 22 and disposed in the peripheral direction of the removing roller. Said toner attached in the brush-like shape was transported by the friction force caused by rotation of the removing roller 21, scraped off by the scraper 24, and returned into the developer reservoir 19. It was observed at the upper area of the magnetic plate 27 on the surface of the electrostatic latent image holding member 14 that the toner was in a fierce turbulence. The toner images thus formed on the electrostatic latent image holding member 14 were transferred on paper (not shown in Fig. 6) by means of the transfer corona charger 25. Then, after thermally fixing by means of fixing equipment (not shown in Fig. 6), printed images were obtained. On the other hand, the toner left on the electrostatic latent image holding member 14 after transferring was transported by the rotation of the electrostatic latent image holding member 14, and collected by the cleaner 26. As a result, sharp images of high image density without showing any non-uniformity of density were obtained. How the electrophotographic apparatus of the present example operates and the effects thereof are the same as explained in Example 1. Example 3 Next, an electrophotographic apparatus will be explained as a third exemplary embodiment with the help of Fig. 9 to Fig. 12. Fig. 9 is a schematic illustration to show the structure of another exemplary embodiment of an electrophotographic apparatus. In Fig. 9, item 14 is a cylindrical electrostatic latent image holding member (30 mm in diameter), which has its surface disposed with an organic photoconductor prepared by dispersing phthalocyanine in a binder resin of polyester group, and rotates at a peripheral speed of 30 mm/s. Item 15 is a non-rotary magnet which is fixed coaxially with said electrostatic latent image holding member 14. There are no particular restrictions imposed on the magnet 15, and a Permanent magnet or an electromagnet, for example, can be used. The peak value of the magnetic flux density on the surface of the electrostatic latent image holding member 14 is -800 Cs (S-pole). Item 16 is a corona charger for charging negatively the electrostatic latent image holding member 14. Item 17 is a grid electrode for controlling the charge potential of the electrostatic latent image holding member 14. Item 18 is signal light for forming electrostatic latent images. Item 19 is a developer reservoir. Item 20 is a developer, e.g. a magnetic mono-component negatively chargeable toner with an average particle diameter of 12 µm. Item 21 is a cylindrical removing roller (16 mm in diameter) made of aluminum, serving as an electrode and rotating at a peripheral speed of 30 mm/s in the direction opposite to the rotation of the electrostatic latent image holding member 14. Item 22 is a non-rotary magnet fixed coaxially with the removing roller 21 and formed of two magnetic poles. There are no specific restrictions imposed on the magnet 22, and a permanent magnet or an electromagnet, for example, can be used. Item 23 is an AC high voltage power source for applying a voltage to the removing roller 21. Item 24 is a scraper made of polyester film for scraping off the toner attached on the removing roller 21. Item 25 is a transfer corona charger for transferring the images, which were formed on the electrostatic latent image holding member by deposition of toner, onto paper. Item 26 is a cleaner for removing the toner that remained on the electrostatic latent image holding member 14 after transferring the images. Fig. 11 shows a chart of the magnetic flux density distribution observed on the surface of the removing roller 21 in the vertical direction of the magnet 22. The peak values of the magnetic flux density measure -600 Gs (N-pole), and -350 Gs (S-pole), respectively. Fig. 21 shows the positional relation between the magnets 15 and 22 both installed inside the electrostatic latent image holding member 14 and the removing roller 21, respectively. The angle  1 that the magnet 15 installed inside the electrostatic latent image holding member 14 makes from the point where the surface of the electrostatic latent image holding member 14 comes closest to that of the removing roller 21 was set to  1 = 35° in the direction opposite to the rotation of the electrostatic latent image holding member 14, while the angle  2 of the north pole of the magnet 22 inside the removing roller 21 being set to  2 = -15° and the angle  3 of the south pole to  3 = + 20°. The range of said angle  1 is desirable to be 0° <  1 < 45° and the range of 10° <  1 < 40°, in particular, is the most suitable range. The range of  2 is desirable to be - 20° <  2 < 0° and the range of - 15° <  2 < - 10°, in particular, is the most suitable range. The range of  3 is desirable to be 0° <  3 < 90° and the range of 10° <  3 < 50°, in particular, is the most suitable range. The composition of the developer used in the present example, e.g. the one component magnetic toner, was 70 % wt. of polyester resin, 25 % wt. of ferrite, 3 % wt. of carbon black, and 2 % wt. of oxycarboxylic acid metal complex with 0.4 % wt. of colloidal silica added further. How the electrophotographic apparatus thus structured operates will be explained hereunder with the help of Fig. 9. The electrostatic latent image holding member 14 was charged to - 500 V by means of the corona charger 16 and the grid electrode 17. (The applied voltage was - 4 kV and the grid electrode voltage was - 500 V.) Then, an electrostatic latent image was formed by irradiation of the laser signal light 18 on said electrostatic latent image holding member 14. At this time, the exposure potential (V r ) of the electrostatic latent image holding member 14 was - 100 V. Next, the mono-component magnetic toner was attached on the surface of said electrostatic latent image holding member 14 in the developer reservoir 19 by the magnetic force of the magnet 15. At this time, the toner was charged to about -3 µC/g. The electrostatic latent image holding member 14 attached with a toner layer passed the front of the removing roller 21, the surface of which was located at a distance of 300 um from that of the electrostatic latent image holding member 14. An AC voltage (1 kHz in frequency) of 750 V 0-p superimposed with a DC voltage of - 300 V having a waveform as shown in Fig. 5 was applied to the removing roller 21 from the high voltage power source 23. While the toner layer on the electrostatic latent image holding member 14 was traveling by passing between the electrostatic latent image holding member 14 and the removing roller 21, the toner attached on the non-image areas of the electrostatic latent image holding member 14 was gradually removed to the side of the removing roller 21. There remained only at the image areas of the electrostatic latent image holding member 14 the toner images with a positive-negative picture reversal. The toner attached on the removing roller 21 which was rotating in the arrow direction was formed into a brush-like shape along the magnetic force which was produced by the magnet 22 and disposed in the peripheral direction of the removing roller 21. The toner attached on the removing roller 21 in a brush-like shape was transported by the friction force due to the rotation of the removing roller 21, scraped off by the scraper 24, and returned into the developer reservoir 19. It was observed at the upper area of the S-pole on the surface of the removing roller 21 that the toner was in a fierce turbulence. The toner images thus formed on the electrostatic latent image holding member 14 were transferred on paper (not shown in Fig. 9) by means of the transfer corona charger 25. Then, after thermally fixing by means of fixing equipment (not shown in Fig. 9), printed images were obtained. On the other hand, the toner left on the electrostatic latent image holding member 14 after transferring was transported by the rotation of the electrostatic latent image holding member 14, and collected by the cleaner 26. As a result, sharp images of high image density without showing any non-uniformity of density were obtained. Accordingly, this particular exemplary embodiment features a structure comprising a fixed and non-rotary magnet, e.g. a magnetic field generating means, which is installed inside a rotary removing roller, and produces two magnetic Poles having Polarity opposite to each other on the surface of the removing roller in the vicinity of the development areas where the electrostatic latent image holding member comes closest to the removing roller. How the electrophotographic apparatus of the present example operates and the effects thereof will be explained in a greater detail with the help of Fig. 10. Fig. 10 is an enlarged view to show schematically the vicinity of the development areas of the electrophotographic apparatus as illustrated in Fig. 9. As shown in Fig. 10, the toner serving as the developer is aligned in a brush-like shape along the magnetic force lines generated by the magnet 22 in the peripheral direction of the removing roller 21 to form a magnetic brush 20b. Therefore, because the transporting force of the toner 20 exerted by the removing roller 21 does not only work on the individual particles of the toner, which are forming the first layer of the toner and in direct contact with the surface of the removing roller 21, but also works on the entire magnetic brush which is a collection of the toner particles put together by magnetic force, the transporting force to carry the toner will be remarkably intensified. Besides, the unevenness in transporting force due to the scattering in frictional force among the individual toner particles will be rectified. As a result, since the low charged toner collected by the removing roller 21 can be removed from the areas vibrated by an AC bias voltage in a forceful and stable manner, excellent Picture quality without any background development and non-uniformity of density can be obtained even under the conditions of high temperature and high humidity or high speed processing. Example 4 Next, a fourth exemplary embodiment for an electrophotographic apparatus will be explained with the help of Fig. 13. Fig. 14, and Fig. 15. The present example is a modification of the previous exemplary embodiment, e.g. Example 3, and the structure thereof is illustrated in Fig. 13. The structure shown in Fig. 13 differs from that of Fig. 9 in the construction of the magnet 22. More specifically, the magnet 22 has one magnetic pole, and a magnetic plate 28 is mounted on the upper side of the magnet 22. As the magnetic plate 28 is used such a substance readily magnetized by an external magnetic field as iron or the like. The other parts of Fig. 13 are the same as those in Fig. 9. Therefore, the same explanation as was made on the symbols used in Fig. 9 applies to those of Fig. 13, and the explanation on the symbols is omitted here. Fig. 14 shows a chart of the magnetic flux density distribution of the magnet 22 and the magnetic plate 27 observed on the surface of the removing roller 21 in the vertical direction. The magnetic plate 28 is magnetized by the magnet 22, and a magnetic pole opposite to the one formed on the surface of the magnet 22 is produced on the surface of the magnetic plate 28. The peak values of the magnetic flux density measure 600 Gs (N-pole), and - 200 Gs (magnetic plate), respectively. Fig. 15 shows the positional relation between the magnet 22 inside the removing roller 21 and the magnet 15 inside the electrostatic latent image holding member 14. The angle that the magnetic 15 installed inside the electrostatic latent image holding member 14 makes from the point where the surface of the electrostatic latent image holding member 14 comes closest to that of the removing roller 21 was set to  1 = 35° in the direction opposite to the rotation of the electrostatic latent image holding member 14, while the angle  2 of the north pole of the magnet 22 inside the removing roller 21 and the angle  3 of the magnetic plate being set to  2 =- 15° and  3 = + 15°, respectively. The range of said angle  1 is desirable to be 0° <  1 < 45° and the range of 10° <  1 < 40°, in particular, is the most suitable range. The range of  2 is desirable to be - 20° <  2 < 0° and the range of - 15° <  2 < - 10°, in particular, is the most suitable range. The range of  3 is desirable to be 0° <  3 < 90° and the range of 10° <  3 < 50°, in particular, is the most suitable range. How the electrophotographic apparatus thus structured operates will be explained hereunder with the help of Fig. 13. The electrostatic latent image holding member 14 was charged to - 500 V by means of the corona charger 16 and the grid electrode 17. (The applied voltage was - 4 kV and the grid electrode voltage was - 500 V.) Then, an electrostatic latent image was formed by irradiation of the laser signal light 18 on said electrostatic latent image holding member 14. At this time, the exposure potential of the electrostatic latent image holding member 14 was - 100 V. The mono-component magnetic toner was attached on the surface of said electrostatic latent image holding member 14 in the developer reservoir 19 by the magnetic force of the magnet 15. Next, the electrostatic latent image holding member 14 attached with said toner layer passed the front of the removing roller 21. An AC voltage (1 kHz in frequency) of 750 V 0-p superimposed with a DC voltage of - 300 V having a waveform as shown in Fig. 5 was applied to the removing roller 21 from the high voltage power source 23. The toner layer on the electrostatic latent image holding member 14 traveled between the electrostatic latent image holding member 14 and the removing roller 21. The toner attached on the non-image areas of the electrostatic latent image holding member 14 was gradually removed to the side of the removing roller 21, and there remained only at the image areas of the electrostatic latent image holding member 14 the toner images with a positive-negative picture reversal. The toner attached on the removing roller 21 which was rotating in the arrow direction was formed into a brush-like shape along the magnetic force which was produced by the magnet 22 and the magnetic plate 28 and disposed in the peripheral direction of the removing roller 21. The said toner attached on the removing roller 21 in a brush-like shape was transported by the friction force due to the rotation of the removing roller 21, scraped off by the scraper 24, and returned into the developer reservoir 19. Besides, it was observed in the upper area of the magnetic plate 28 on the surface of the removing roller 21 that the toner was in a fierce turbulence. The toner images thus formed on the electrostatic latent image holding member 14 were transferred on paper (not shown in Fig. 13) by means of the transfer corona charger 25. Then, after thermally fixing by means of fixing equipment (not shown in Fig. 13), Printed images were obtained. On the other hand, the toner left on the electrostatic latent image holding member 14 after transferring was transported by the movement of the electrostatic latent image holding member 14, and collected by the cleaner 26. As a result, sharp images of without showing any background development or non-uniformity of images were obtained. How the electrophotographic apparatus of the present example operates and the effects thereof are the same as explained in Example 3. Example 5 Next, an electrophotographic apparatus according to the present invention will be explained as a fifth exemplary embodiment with the help of Fig. 16 and Fig. 17. Fig. 16 is a schematic illustration to show the structure of the present example. The structure shown in Fig. 16 differs from that of Fig. 1 in the means to produce magnetic fields on the surface of the removing roller. More specifically, a non-rotary magnet 22 installed inside the removing roller 21 and fixed thereto coaxially has two poles. There are no specific restrictions imposed on the magnet 22, and a permanent magnet or an electromagnet, for example, can be used. Fig. 4 shows a chart of the distribution of the magnetic fluxes produced by a magnet 15 and observed on the surface of the electrostatic latent image holding member 14 in the vertical direction. Fig. 11 shows a chart of the distribution of the magnetic fluxes produced by the magnet 22 and observed on the surface of the removing roller 21 in the vertical direction. Fig. 17 shows the positional relation between the magnet 15 inside the electrostatic latent image holding member 14 and the magnet 22 inside the removing roller 21. The angle that the S-pole of the magnet 15 installed inside the electrostatic latent image holding member 14 makes from the point where the surface of the electrostatic latent image holding member 14 comes closest to that of the removing roller 21 was set to  1 = 40° in the direction opposite to the rotation of the electrostatic latent image holding member 14, while the angle  2 of the N-pole of the same being set to  2 = 10°. The angle that the N-pole of the magnet 22 installed inside the removing roller 21 makes from the point where the surface of the removing roller comes closest to that of the electrostatic latent image holding member 14 was set to  3 = - 15° in the direction opposite to the rotation of the removing roller, while the angle  4 of the S-pole of the same being set to  4 = 20°. The range of said angle  1 is desirable to be 15° <  1 < 50° and the range of 20° <  1 < 45°, in particular, is the most suitable range. The range of  2 is desirable to be 0° <  2 < 30° and the range of 5° <  2 < 20°, in particular, is the most suitable range. The range of  3 is desirable to be - 30° <  3 < 10° and the range of - 20° <  3 < 0°, in particular, is the most suitable range. The range of  4 is desirable to be 0° <  4 < 30° and the range of 5° <  4 < 25°, in particular, is the most suitable range. How the electrophotographic apparatus thus structured operates will be explained hereunder with the help of Fig. 16. The electrostatic latent image holding member 14 was charged to - 500 V by means of the corona charger 16 and the grid electrode 17. (The applied voltage was - 4 kV and the grid electrode voltage was - 500 V.) Then, an electrostatic latent image was formed by irradiation of the laser signal light 18 on said electrostatic latent image holding member 14. At this time, the exposure potential of the electrostatic latent image holding member 14 was - 100 V. Mono-component magnetic toner was attached on the surface of said electrostatic latent image holding member 14 in the developer reservoir 19 by the magnetic force of the magnet 15. Next, the toner attached on the electrostatic latent image holding member 14 was aligned in the peripheral direction of the electrostatic latent image holding member 14 along the magnetic field produced by the magnet 15 to form a magnetic brush, and the brush-like toner was transported by the friction force due to the rotation of the electrostatic latent image holding member 14. Then, the electrostatic latent image holding member 14 attached with said toner layer passed the front of the removing roller 21. An AC voltage (1 kHz in frequency) of 750 V 0-p superimposed with a DC voltage of - 300 V having a waveform as shown in Fig. 5 was applied to the removing roller 21 from the high voltage power source 23. The toner layer on the electrostatic latent image holding member 14 traveled between the electrostatic latent image holding member 14 and the removing roller 21, and the toner attached on the non-image areas of the electrostatic latent image holding member 14 was gradually removed to the side of the removing roller 21. There remained only at the image areas of the electrostatic latent image holding member 14 the toner images with a positive-negative picture reversal. On the other hand, the toner attached on the removing roller 21 was formed into a brush-like shape along the magnetic field produced in the peripheral direction of the removing roller. The said toner attached in a brush-like shape was transported by the frictional force due to the rotation of the removing roller 21, scraped off by the scraper 24, and returned into the developer reservoir 19. Besides, it was observed in the upper area of the magnetic plate 27 on the surface of the removing roller 21 that the toner was in a fierce turbulence. The toner images thus formed on the electrostatic latent image holding member 14 were transferred on paper (not shown in Fig. 16) by means of the transfer corona charger 25. Then, after thermally fixing by means of fixing equipment (not shown in Fig. 16), printed images were obtained. On the other hand, the toner left on the electrostatic latent image holding member 14 after transferring was transported by the movement of the electrostatic latent image holding member 14, and collected by the cleaner 26. As a result, sharp images of high image density and non-uniformity in image density without showing any background development or image hysteresis were obtained. Accordingly, the present example features a structure comprising a magnetic field generating means installed inside an electrostatic latent image holding member for producing two magnetic poles having polarity different from each other on the surface of said electrostatic latent image holding member in the vicinity of developing areas where the electrostatic latent image holding member comes closest to a removing roller. and a magnetic field generating means installed inside the removing roller for producing two magnetic poles having polarity different from each other on the surface of the removing roller in the vicinity of the developing areas where the electrostatic latent image holding member comes opposite to the removing roller. Therefore, because the toner supplied to the electrostatic latent image holding member 14 can be fed abundantly and in a stabilized manner to the development areas and further the toner collected by the removing roller 21 can be removed sufficiently and in a stabilized manner from the area vibrating due to an AC bias voltage, images of excellent picture quality with a high image density and not showing any background development or non-uniformity of density even under the conditions of high temperature, high humidity, and high speed processing. Example 6 Next, an electrophotographic apparatus according to the present invention will be explained as a sixth exemplary embodiment with the help of Fig. 18 and Fig. 19. The present example is a modification of the previous exemplary embodiment, e.g. Example 5, and the structure there of is illustrated in Fig. 18. The structure shown in Fig. 18 differs from that of Fig. 1 in the means to produce magnetic field on the surface of the removing roller 21. More specifically, the difference is in having a magnetic plate 28 mounted on the upper side of the non-rotary magnet 22 installed inside the removing roller 21 and fixed thereto coaxially. Fig. 4 shows a chart of the distribution of the magnetic fluxes produced by the magnet 15 and observed on the surface of the electrostatic latent image holding member 14 in the vertical direction. Fig. 14 shows a chart of the distribution of the magnetic fluxes produced by the magnet 22 and observed on the surface of the removing roller 21 in the vertical direction. Fig. 19 shows the positional relation between the magnet 15 inside the electrostatic latent image holding member 14 and the magnet 22 inside the removing roller 21. The angle that the S-pole of the magnet 15 installed inside the electrostatic latent image holding member 14 makes from the point where the surface of the electrostatic latent image holding member 14 comes closest to that of the removing roller 21 was set to  1 = 40° in the direction opposite to the rotation of the electrostatic latent image holding member 14, while the angle  2 of the N-pole of the same being set to  2 = 10°. The angle that the N-pole of the magnet 22 installed inside the removing roller 21 makes from the point where the surface of the removing roller comes closest to that of the electrostatic latent image holding member 14 was set to  3 = - 15° in the direction opposite to the rotation of the removing roller, while the angle  4 of the magnetic plate being set to  4 = 15°. The range of said angle  1 is desirable to be 15° <  1 < 50° and the range of 20° <  1 < 45°, in particular, is the most suitable range. The range of  2 is desirable to be 0° <  2 < 30° and the range of 5° <  2 < 20°, in particular, is the most suitable range. The range of  3 is desirable to be - 30° <  3 < 10° and the range of - 20° <  3 < 0°, in particular, is the most suitable range. The range of  4 is desirable to be 0° <  4 < 30° and the range of 5° <  4 < 25°, in particular, is the most suitable range. How the electrophotographic apparatus thus structured operates will be explained hereunder with the help of Fig. 18. The electrostatic latent image holding member 14 was charged to - 500 V by means of the corona charger 16 and the grid electrode 17. (The applied voltage was - 4 kV and the grid electrode voltage was - 500 V.) Then, an electrostatic latent image was formed by irradiation of the laser signal light 18 on said electrostatic latent image holding member 14. At this time, the exposure potential of the electrostatic latent image holding member 14 was - 100 V. One-component magnetic toner was attached on the surface of said electrostatic latent image holding member 14 in the developer reservoir 19 by the magnetic force of the magnet 15. Next, the toner attached on the electrostatic latent image holding member 14 was aligned in the peripheral direction of the electrostatic latent image holding member 14 along the magnetic field produced by the magnet 15 to form a magnetic brush, and the brush-like toner was transported by the friction force due to the rotation of the electrostatic latent image holding member 14. Then, the electrostatic latent image holding member 14 attached with said toner layer passed the front of the removing roller 21. An AC voltage (1 kHz in frequency) of 750 V 0-p superimposed with a DC voltage of - 300 V having a waveform as shown in Fig. 5 was applied to the removing roller 21 from the high voltage power source 23. The toner layer on the electrostatic latent image holding member 14 traveled between the electrostatic latent image holding member 14 and the removing roller 21, and the toner attached on the non-image areas of the electrostatic latent image holding member 14 was gradually removed to the side of the removing roller 21. There remained only at the image areas of the electrostatic latent image holding member 14 the toner images with a positive-negative picture reversal. The toner attached on the removing roller 21 was formed into a brush-like shape along the magnetic field produced by the magnet 22 inside the removing roller in the peripheral direction of the removing roller. The said toner attached in a brush-like shape was transported by the friction force due to the rotation of the removing roller 21, scraped off by the scraper 24, and returned into the developer reservoir 19. Besides, it was observed in the upper areas of both the S-pole inside the electrostatic latent image holding member 14 and the magnetic plate inside the removing roller 21 that the toner was in a fierce turbulence. The toner images thus formed on the electrostatic latent image holding member 14 were transferred on paper (not shown in Fig. 18) by means of the transfer corona charger 25. Then, after thermally fixing by means of fixing equipment (not shown in Fig. 18), printed images were obtained. On the other hand, the toner left on the electrostatic latent image holding member 14 after transferring was transported by the rotation of the electrostatic latent image holding member 14, and collected by the cleaner 26. As a result, sharp images of high image density and of non-uniformity in density without showing any background development or image hysteresis were obtained. How the electrophotographic apparatus of the present example operates and the effects thereof are the same as explained in Example 5. Example 7 Next, an electrophotographic apparatus according to the present invention will be explained as a seventh exemplary embodiment with the help of Fig. 20 and Fig. 21. The present example is a modification of the previous exemplary embodiment, e.g. Example 5, and the structure there of is illustrated in Fig. 20. The structure shown in Fig. 20 differs from that of Fig. 6 in the means to produce magnetic field on the surface of the removing roller 21. More specifically, the difference is in having the magnet 22 installed inside the removing roller 21 formed of two magnetic poles. Fig. 7 shows a chart of the distribution of the magnetic fluxes produced by the magnet 15 and the magnetic plate 27 and observed on the surface of the electrostatic latent image holding member 14 in the vertical direction. Fig. 11 shows a chart of the distribution of the magnetic fluxes produced by the magnet 22 and observed on the surface of the removing roller 21 in the vertical direction. Fig. 21 shows the positional relation between the magnet 15 inside the electrostatic latent image holding member 14 and the magnet 22 inside the removing roller 21. The angle that the magnetic plate 27 installed inside the electrostatic latent image holding member 14 makes from the point where the surface of the electrostatic latent image holding member 14 comes closest to that of the removing roller 21 was set to  1 = 40° in the direction opposite to the rotation of the electrostatic latent image holding member 14, while the angle  2 of the N-pole of the magnet 15 inside the electrostatic latent image holding member 14 being set to  2 = 10°. The angle that the N-pole of the magnet 22 installed inside the removing roller 21 makes from the point where the surface of the removing roller comes closest to that of the electrostatic latent image holding member 14 was set to  3 = - 15° in the direction opposite to the rotation of the removing roller, while the angle  4 of the S-pole of the magnet 22 being set to  4 = + 20°. The range of said angle  1 is desirable to be 15° <  1 < 50° and the range of 20° <  1 < 45°, in particular, is the most suitable range. The range of  2 is desirable to be 0° <  2 < 30° and the range of 5° <  2 < 20°, in particular, is the most suitable range. The range of  3 is desirable to be - 30° <  3 < 10° and the range of - 20° <  3 < 0°, in particular, is the most suitable range. The range of  4 is desirable to be 0° <  4 < 30° and the range of 5° <  4 < 25°, in particular, is the most suitable range. How the electrophotographic apparatus thus structured operates will be explained hereunder with the help of Fig. 20. The electrostatic latent image holding member 14 was charged to - 500 V by means of the corona charger 16 and the grid electrode 17. (The applied voltage was - 4 kV and the grid electrode voltage was - 500 V.) Then, an electrostatic latent image was formed by irradiation of the laser signal light 18 on said electrostatic latent image holding member 14. At this time, the exposure potential of the electrostatic latent image holding member 14 was - 100 V. Mono-component magnetic toner was attached on the surface of said electrostatic latent image holding member 14 in the developer reservoir 19 by the magnetic force of the magnet 15 installed inside the electrostatic latent image holding member 14. Next, the toner attached on the electrostatic latent image holding member 14 was aligned in the peripheral direction along the magnetic field produced by the magnet 15 inside the electrostatic latent image holding member 14 to form a magnetic brush, and the brush-like toner was transported by the friction force due to the rotation of the electrostatic latent image holding member 14. Then, the electrostatic latent image holding member 14 attached with said toner layer passed the front of the removing roller 21. An AC voltage (1 kHz in frequency) of 750 V 0-p superimposed with a DC voltage of - 300 V having a waveform as shown in Fig. 5 was applied to the removing roller 21 from the high voltage power source 23. The toner layer on the electrostatic latent image holding member 14 traveled between the electrostatic latent image holding member 14 and the removing roller 21, and the toner attached on the non-image areas of the electrostatic latent image holding member 14 was gradually removed to the side of the removing roller 21. There remained only at the image areas of the electrostatic latent image holding member 14 the toner images with a positive-negative picture reversal. The toner attached on the removing roller 21 was formed into a brush-like shape along the magnetic field produced by the magnet 22 inside the removing roller in the peripheral direction of the removing roller. The said toner attached in a brush-like shape was transported by the friction force due to the rotation of the removing roller 21, scraped off by the scraper 24, and returned into the developer reservoir 19. Besides, it was observed in the upper areas of both the S-pole inside the electrostatic latent image holding member 14 and the magnetic Plate inside the removing roller 21 that the toner was in a fierce turbulence. The toner images thus formed on the electrostatic latent image holding member 14 were transferred on paper (not shown in Fig. 20) by means of the transfer corona charger 25. Then, after thermally fixing by means of fixing equipment (not shown in Fig. 20), printed images were obtained. As a result, sharp images of high image density and of non-uniformity in density without showing any background development or image hysteresis were obtained. On the other hand, the toner left on the electrostatic latent image holding member 14 after transferring was transported by the rotation of the electrostatic latent image holding member 14, and collected by the cleaner 26. How the electrophotographic apparatus of the present example operates and the effects thereof are the same as explained in Example 5. Example 8 Next, an electrophotographic apparatus whereby excellent images of high image density without showing any non-uniformity of image density even at a higher printing speed are obtainable will be explained as an exemplary embodiment with the help of Fig. 22. Fig. 22 shows the structure of an electrophotographic apparatus having a Processing speed of 180 mm/s. The structure of Fig. 22 differs from that of Fig. 1 in the number of magnetic poles of the magnet 15 installed inside the electrostatic latent image holding member 14 and the roughness of the surface of the electrostatic latent image holding member 14. More specifically, the number of magnetic poles of the magnet 15 is one and further the surface of the electrostatic latent image holding member 14 is treated by sand blasting to have roughness of 0.8 µm with the present example. On account of said blasting treatment, the friction force between the surface of the electrostatic latent image holding member 14 and the developer, e.g. the toner has been effectively increased. Other parts of the structure shown in Fig. 22 are the same as those of Fig. 1, and the same explanation as made on the symbols of Fig. 1 applies to the ones of Fig. 22. How the electrophotographic apparatus thus structured operates will be explained hereunder with the help of Fig. 22. The electrostatic latent image holding member 14 was charged to - 500 V by by means of the corona charger 16 and the grid electrode 17. (The applied voltage was - 6 kV and the grid electrode voltage was - 500 V.) Then, an electrostatic latent image was formed by irradiation of the laser signal light 18 on said electrostatic latent image holding member 14. At this time, the exposure potential of the electrostatic latent image holding member 14 was - 100 V. Mono-component magnetic toner was attached on the surface of said electrostatic latent image holding member 14 in the developer reservoir 19 by the magnetic force of the magnet 15. The toner attached on the electrostatic latent image holding member 14 was transported without any slipping by the strong friction force working between the toner and the surface of the electrostatic latent image holding member 14. Then, the electrostatic latent image holding member 14 attached with said toner layer passed the front of the removing roller 21. An AC voltage (1 kHz in frequency) of 750 V 0-p superimposed with a DC voltage of - 300 V having a waveform as shown in Fig. 5 was applied to the removing roller 21 from the high voltage power source 23. The toner layer on the electrostatic latent image holding member 14 traveled between the electrostatic latent image holding member 14 and the removing roller 21, and the toner attached on the non-image areas of the electrostatic latent image holding member 14 was gradually removed to the side of the removing roller 21. There remained only at the image areas of the electrostatic latent image holding member 14 the toner images with a positive-negative picture reversal. The toner attached on the removing roller 21 was transported by the rotation of the removing roller 21 in the arrow direction, scraped off by the scraper 24, and returned into the developer reservoir 19. The toner images thus formed on the electrostatic latent image holding member 14 were transferred on paper (not shown in Fig. 22) by means of the transfer corona charger 25. Then, after thermally fixing by means of fixing equipment (not shown in Fig. 22), printed images were obtained. On the other hand, the toner left on the electrostatic latent image holding member 14 after transferring was transported by the rotation of the electrostatic latent image holding member 14, and collected by the cleaner 26. As a result, sharp images of high image density and non-uniformity in image density were obtained. As explained in the foregoing, the structure of the present example features a means to multiply the friction force between the surface of the electrostatic latent image holding member 14 and the developer. Accordingly, on account of the increased friction force between the electrostatic latent image holding member and the toner, the toner can be transported by the rotation of the electrostatic latent image holding member without any slipping, and the capability of supply and transportation of toner can be greatly enhanced, and further the problem of uneven transportation of toner due to slippage can be solved. Therefore, because the toner supplied to the surface of the electrostatic latent image holding member can be fed to development areas in abundance and in a stabilized manner, excellent image quality of high image density and free of non-uniformity in image density can be realized even under the conditions of high temperature, high humidity, and high speed processing. Besides, even when the surface roughness of the electrostatic latent image holding member 14 is 0.5, it was possible to gain the same excellent results as above. Further, although the surface of the electrostatic latent image holding member 14 was treated by blasting with the present example, it is also possible to gain the same effect by making fine grooves on the surface of the electrostatic latent image holding member 14. More specifically, the friction force between the surface of the electrostatic latent image holding member 14 and the toner is increased remarkably by grooving. As a result, the toner supplied is transported without slippage and sharp images of high image density and free of non-uniformity in image density are obtained. Example 9 Next, an electrophotographic apparatus whereby excellent images of high image density without showing any non-uniformity of image density even at a higher printing speed are obtainable will be explained as another exemplary embodiment with the help of Fig. 23 and Fig. 24. Fig. 23 shows the structure of an electrophotographic apparatus having a processing speed of 180 mm/s. Fig. 24 is an enlarged cross-sectional view of the rise and fall of the surface of the removing roller 21 which composes the electrophotographic apparatus shown in Fig. 23. The structure of Fig. 23 differs from that of Fig. 9 in the number of magnetic Poles of the magnet 22 installed inside the removing roller 21 and the roughness of the surface of the removing roller 21. More specifically, the number of magnetic poles of the magnet 22 is one and further the surface of the removing roller 21 has fine grooves running in parallel with the axial direction on the surface of the removing roller as shown in Fig. 24. How the electrophotographic apparatus thus structured operates will be explained hereunder with the help of Fig. 23. The electrostatic latent image holding member 14 was charged to - 500 V by means of the corona charger 16 and the grid electrode 17. (The applied voltage was - 6 kV and the grid electrode voltage was - 500 V.) Then, an electrostatic latent image was formed by irradiation of the laser signal light 18 on said electrostatic latent image holding member 14. At this time, the exposure potential of the electrostatic latent image holding member 14 was - 100 V. Mono-component magnetic toner was attached on the surface of said electrostatic latent image holding member 14 in the developer reservoir 19 by the magnetic force of the magnet 15. Then, the electrostatic latent image holding member 14 attached with said toner layer passed the front of the removing roller 21. An AC voltage (1 kHz in frequency) of 750 V 0-p superimposed with a DC voltage of - 300 V having a waveform as shown in Fig. 5 was applied to the removing roller 21 from the high voltage power source 23. The toner layer on the electrostatic latent image holding member 14 traveled between the electrostatic latent image holding member 14 and the removing roller 21, and the toner attached on the non-image areas of the electrostatic latent image holding member 14 was gradually removed to the side of the removing roller 21. There remained only at the image areas of the electrostatic latent image holding member 14 the toner images with a positive-negative picture reversal. The toner attached on the removing roller 21 was transported by the rotation of the removing roller 21 in the arrow direction without slippage on account of the strong friction force caused by the grooves made on the surface of the removing roller 21, scraped off by the scraper 24, and returned into the developer reservoir 19. The toner images thus formed on the electrostatic latent image holding member 14 were transferred on paper (not shown in Fig. 23) by means of the transfer corona charger 25. Then, after thermally fixing by means of fixing equipment (not shown in Fig. 23), printed images were obtained. On the other hand, the toner left on the electrostatic latent image holding member 14 after transferring was transported by the rotation of the electrostatic latent image holding member 14, and collected by the cleaner 26. As a result, sharp images of high image density and non-uniformity in image density were obtained. As explained in the foregoing, the structure of the present example features a means to multiply the friction force between the surface of the electrostatic latent image holding member 14 and the toner, e.g. the developer. Accordingly, on account of the increased friction force of the removing roller against the toner, the toner can be transported by the rotation of the removing roller without any slipping, and the collection capability of toner can be greatly enhanced, and further the problem of uneven transportation of toner due to slippage can be solved. Therefore, because the slightly charged toner collected by the removing roller can be removed from the areas vibrated by an AC bias voltage sufficiently and in a stabilized manner, excellent image quality of high image density and free of non-uniformity in image density can be realized even under the conditions of high temperature, high humidity and high speed processing. Besides, it is possible to make the roughness of the surface of the removing roller 21 more than 0.5 um by blasting or to have the surface of the removing roller 21 disposed with a conductive layer of resin mulled together with carbon for increasing the friction force between the surface of the removing roller 21 and the toner remarkably. As a result, the toner collected is transported without slippage and sharp images free of background development and non-uniformity in image density are obtained. Example 10 Next, an electrophotographic apparatus whereby excellent images of high image density without showing any non-uniformity of image density even at a higher printing speed are obtainable will be explained as another exemplary embodiment with the help of Fig. 25. Fig. 25 shows the structure of an electrophotographic apparatus having a processing speed of 180 mm/s. The structure of Fig. 25 differs from that of Fig. 1 in the roughness of the surface of the electrostatic latent image holding member 14. More specifically, the surface of the electrostatic latent image holding member 14 is treated by blasting to have roughness of 0.5 µm. On account of said blasting treatment, the friction force between the surface of the electrostatic latent image holding member 14 and the developer, e.g. the toner is effectively increased. Other parts of the structure shown in Fig. 25 are the same as those of Fig. 1, and the same explanation as made on the symbols of Fig. 1 applies to the ones of Fig. 25. The structure of the present example comprises a magnetic field generating means installed inside the electrostatic latent image holding member 14 for producing two magnetic poles, and a means for increasing the friction force between the surface of the electrostatic latent image holding member 14 and the developer disposed on the electrostatic latent image holding member. Accordingly, because the toner attached on the electrostatic latent image holding member can be transported sufficiently to the developing areas by magnetic force and the toner can be transported by the rotation of the electrostatic latent image holding member without any slipping on account of the increased friction force between the electrostatic latent image holding member and the toner, the capability of supply and transportation of toner can be greatly enhanced, and further the problem of uneven transportation of toner due to slippage can be solved. Therefore, because the toner supplied to the surface of the electrostatic latent image holding member can be fed to developing areas in abundance and in a stabilized manner, excellent image quality of high image density and free of non-uniformity in image density can be realized even under the conditions of high temperature, high humidity, and high speed processing. Example 11 Next, an electrophotographic apparatus whereby excellent images of high image density without showing any non-uniformity of image density even at a higher printing speed are obtainable will be explained as still another exemplary embodiment with the help of Fig. 26. Fig. 26 shows the structure of an electrophotographic apparatus having a processing speed of 180 mm/s. The structure of Fig. 26 differs from that of Fig. 9 in the roughness of the surface of the removing roller 21. More specifically, the surface of the removing roller 21 is treated by sand blasting to have roughness of 0.5 µm. The structure of the present example comprises a magnetic field generating means installed inside the removing roller for producing two magnetic poles, and a means for increasing the friction force between the surface of the removing roller and the toner, e.g. the developer disposed on the removing roller. Accordingly, the toner collected to the removing roller can be removed sufficiently from the developing areas by magnetic force and further the capability of toner collection can be greatly enhanced because the friction force between the removing roller and the toner is increased and the toner is transported by the rotation of the removing roller without slippage, and still further the problem of uneven transportation of the toner due to slippage can be solved. Therefore, because the slightly charged toner collected by the removing roller can be removed from the areas vibrating by an AC bias voltage can be removed sufficiently and in a stabilized manner, excellent image quality of high image density and free of non-uniformity in image density can be realized even under the conditions of high temperature, high humidity, and high speed processing. Example 12 Next, an electrophotographic apparatus whereby excellent images of high image density without showing any non-uniformity of image density even at a higher printing speed are obtainable will be explained as another exemplary embodiment of the present invention with the help of Fig. 27. Fig. 27 shows the structure of an electrophotographic apparatus having a processing speed of 180 mm/s. The structure of Fig. 27 differs from that of Fig. 16 in the roughness of the surfaces of the electrostatic latent image holding member 14 and the removing roller 21. More specifically, the surfaces of the electrostatic latent image holding member 14 and the removing roller 21 are treated by blasting to have roughness of 0.5 µm, respectively. The structure of the present example comprises a magnetic field generating means for producing two magnetic poles of polarity different from each other on the surface of the electrostatic latent image holding member, a means for increasing the friction force of the surface of the electrostatic latent image holding member, a magnetic field generating means installed inside the removing roller 21 for producing two magnetic poles, and a means for increasing the friction force between the surface of the removing roller and the developer, e.g. the developer disposed on the removing roller. Accordingly, because the toner attached on the electrostatic latent image holding member can be transported sufficiently to the developing areas by magnetic force and the toner can be transported by the rotation of the electrostatic latent image holding member without any slipping on account of the increased friction force between the electrostatic latent image holding member and the toner, the capability of supply and transportation of toner can be greatly enhanced. Further, the capability of toner collection can be greatly enhanced because the friction force between the removing roller and the toner is increased and the toner is transported by the rotation of the removing roller without slipping, and the problem of uneven transportation of toner due to slippage can be also solved. Therefore, because the toner supplied to the surface of the electrostatic latent image holding member can be fed to developing areas in abundance and in a stabilized manner, the slightly charged toner collected by the removing roller can be removed from the areas vibrating by an AC bias voltage can be removed sufficiently and in a stabilized manner, excellent image quality free of background development and non-uniformity in image density can be realized even under the conditions of high temperature, high humidity, and high speed processing. The foregoing examples according to the invention are merely representing typical exemplary embodiments of the present invention in whatsoever and should not be interpreted as restricting the present invention. For example, it is also possible to build an electrophotographic apparatus of the structure appropriately combining such a variety of means as producing magnetic field from two magnetic poles having polarity different from each other on the surface of an electrostatic latent image holding member, increasing the friction force of the surface of said electrostactic latent image holding member, producing two magnetic poles having polarity different from each other on the surface of a removing roller, increasing the friction force of the surface of said removing roller, and the like.

Claims: An electrophotographic apparatus comprising: a magnetic developer (20), an electrostatic latent image holding member (14) rotating in a specified direction, a removing roller (21) which is placed at a position with a specified distance apart from a surface of said electrostatic latent image holding member, a developer reservoir (19) for supplying said magnetic developer (20) to the surface of said electrostatic latent image holding member (14), a means (23) for applying an AC voltage to said removing roller (21) to remove the magnetic developer staying on non-image areas of said electrostatic latent image holding member, a first magnetic field generating means (15,27) installed inside said electrostatic latent image holding member (14) for producing two magnetic poles of different polarity on the surface of said electrostatic latent image holding member in a vicinity of developing areas where said electrostatic latent image holding member (14) comes closest to said removing roller (21), and a second magnetic field generating means (22,28) installed inside the removing roller (21) for producing two magnetic poles of different polarity on a surface of said removing roller in the vicinity of developing areas where said electrostatic latent image holding member (14) comes closest to said removing roller (21). characterized by said removing roller (21) rotating such that a portion of its surface moves in a direction opposite to the movement of a surface portion of said electrostatic latent image holding member (14), at a point where said removing roller (21) and said electrostatic latent image holding member (14) come closest to each other; the magnetic pole located at the downstream side of the first magnetic field generating means (19,27) with respect to the direction of rotation of the electrostatic latent image holding member (14), having the same polarity as the magnetic pole located at the upstream side of the second magnetic field generating means (22,28) with respect to the direction of rotation of said removing roller (21), and said magnetic pole located at the downstream side of said first magnetic field generating means (15,27) with respect to the direction of rotation of the electrostatic late image holding member (14) being located opposite to said magnetic pole being located at the upstream side of the second magnetic field generating means (22,28) with respect to the direction of rotation of said removing roller (21). Electrophotographic apparatus according to claim 1, wherein the magnetic pole being located at the downstream side of the first magnetic field generating means (15,27) with respect to the direction of rotation of the electrostatic latent image holding member (14) is located at a direction having an angle in the range of 0° to +30° with the direction of the area where said electrostatic latent image holding member (14) comes closest to said removing roller (21), said angle being measured in the direction opposite to the rotation of said electrostatic latent image holding member (14), and the magnetic pole located at the upstream side of the second magnetic field generating means (22,28) with respect to the direction of rotation of the removing roller (21) is located at a direction having an angle in the range of -30° to +10° with the direction of the area where said electrostatic latent image holding member (14) comes closest to said removing roller (21), said angle being measured in the direction opposite to the rotation of said removing roller (21). Electrophotographic apparatus according to claim 1, wherein said first magnetic field generating means (15,27) installed inside said electrostatic latent image holding member (14) comprises a magnet, and said second magnetic field generating means (22, 28) installed inside said removing roller (21) comprises a further magnet. Electrophotographic apparatus according to claim 1, wherein said first magnetic field generating means (15,27) installed inside said electrostatic latent image holding member (14) comprises a magnet (15) for producing one magnetic pole and a substance (27) which can be magnetized by a magnetic field for producing the other magnetic pole, said magnet (15) being located at the downstream side of said first magnetic field generating means (15,27) with respect to the direction of rotation of said electrostatic latent image holding member (14), and said substance (27) being located at the upstream side of said first magnetic field generating means (15,27) with respect to the direction of rotation of said electrostatic latent image holding member (14). Electrophotographic apparatus according to claim 1, wherein said second magnetic field generating means (22,28) installed inside said removing roller (21) comprises a magnet (22) for producing one magnetic pole and a substance (28) which can be magnetized by a magnetic field for producing the other magnetic pole, said magnet (22) being located at the upstream side of said second magnetic field generating means (22,28) with respect to the direction of rotation of said removing roller (21), and said substance (28) being located at the downstream side of said second magnetic field generating means (22,28) with respect to the direction of rotation of said removing roller (21). Electrophotographic apparatus according to claim 1, wherein the surface of said electrostatic latent image holding member (14) is provided with a first means for increasing friction force against said developer 20. Electrophotographic apparatus according to claim 6, wherein said first means for increasing friction force are fine grooves provided in the surface of said electrostatic latent image holding member (14). Electrophotographic apparatus according to claim 6, wherein said first means for increasing friction force is a roughness on the surface of said electrostatic latent image holding member (14) exceeding 0.5 µm inclusive. Electrophotographic apparatus according to claim 1, wherein the surface of said removing roller (21) is provided with a second means for increasing friction force against said developer (20). Electrophotographic apparatus according to claim 9, wherein said second means for increasing friction force are fine grooves provided on the surface of said removing roller (21). Electrophotographic apparatus according to claim 9, wherein said second means for increasing friction force is roughness on the surface of said removing roller (21) exceeding 0.5 µm inclusive.

Inventors: AIZAWA MASAHIRO, HAYASHI KAZUMASA, KOMAKINE HIROSHI, TERADA HIROSHI, YAMAMOTO HAJIME, AIZAWA, MASAHIRO, HAYASHI, KAZUMASA, KOMAKINE, HIROSHI, TERADA, HIROSHI, YAMAMOTO, HAJIME
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1994
Main classification: G03G15
IPC codes: G03G15